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Tailoring the electrochemical activity of magnesium chromium oxide towards Mg batteries through control of size and crystal structure.

Research paper by Linhua L Hu, Ian D ID Johnson, Soojeong S Kim, Gene M GM Nolis, John W JW Freeland, Hyun Deog HD Yoo, Timothy T TT Fister, Liam L McCafferty, Thomas E TE Ashton, Jawwad A JA Darr, Jordi J Cabana

Indexed on: 20 Dec '18Published on: 20 Dec '18Published in: Nanoscale



Abstract

Chromium oxides with the spinel structure have been predicted to be promising high voltage cathode materials in magnesium batteries. Perennial challenges involving the mobility of Mg2+ and reaction kinetics can be circumvented by nano-sizing the materials in order to reduce diffusion distances, and by using elevated temperatures to overcome activation energy barriers. Herein, ordered 7 nm crystals of spinel-type MgCr2O4 were synthesized by a conventional batch hydrothermal method. In comparison, the relatively underexplored Continuous Hydrothermal Flow Synthesis (CHFS) method was used to make highly defective sub-5 nm MgCr2O4 crystals. When these materials were made into electrodes, they were shown to possess markedly different electrochemical behavior in a Mg2+ ionic liquid electrolyte, at moderate temperature (110 °C). The anodic activity of the ordered nanocrystals was attributed to surface reactions, most likely involving the electrolyte. In contrast, evidence was gathered regarding the reversible bulk deintercalation of Mg2+ from the nanocrystals made by CHFS. This work highlights the impact on electrochemical behavior of a precise control of size and crystal structure of MgCr2O4. It advances the understanding and design of new cathode materials for Mg-based batteries.